It depends on the submarine. If measure the distance from the top a fully extended periscope to the bottom of the boat you will get the "Depth of the Keel" at which the periscope is out of the water. Generally between 30 feet and 70 feet.
Yes sonar can be used at periscope depth. Surface ships also have sonar arrays on them. They are usually used to detect submarines.
A periscope.
Google it for the diagram and u will understand why.
To see over walls and in submarines
A Periscope or Radar
On the newer class submarines that don't employ optics, they're called "Photonics Masts". But it's still a Periscope.
periscope
They were used in the first world war in submarines. The are used now also for submarines and also war tanks. The outer coating of the periscope for the submarines were firm and waterproof for protection from the water pressure. As for the war tank the periscope is able to turn 360 degrees.
They use Radar , Sonar, and at periscope depth- optical range finders, the tech manual for the latter is over 300 pages, so its a skilled craft to operate these specialized sights.
PERISCOPE
The Captain used the periscope to locate the enemy ships.A periscope is the eye of a submarine.
Basically to see around corners, do it twice and you have the device that's common on submarines.